A natural draft dry cooling tower has excellent water-saving and energy-saving properties with zero water consumption and zero draught fan power consumption, and thus has gradually become a main cooling device for the circulating water of a thermal power generating unit in the Northwest, North China and other areas with dry and rare water. The natural draft dry cooling tower, hereinafter referred to as a dry cooling tower, is composed of cooling radiators and a towerbody, wherein the radiators are composed of finned tube bundles. The finned tube bundles below the tower body can be either circumferentially arranged around tower to form cooling delta units, or horizontally arranged below the tower body to form A-shaped framework cooling units.
In the dry cooling tower with vertical radiators outside tower, the cooling delta unit is composed of two cooling columns connected in parallel, each cooling column is composed of 3-4 cooling tube bundles connected in series, and the conventional cooling tube bundle is a finned tube bundle with 4 or 6 rows of base tubes. In the dry cooling tower with horizontal radiators inside tower, the A-shaped framework cooling unit is composed of two cooling columns connected in parallel, and each cooling column includes 2-4 cooling tube bundles connected in series.
The circulating water flows in the finned tube bundles of the dry cooling tower, so as to transmit the heat to the ambient air flowing by the fins in a convective heat transfer manner. The existing research shows that the ambient natural crosswind has a direct influence on the aerodynamic field around tower bottom air inlet and the aerodynamic field around tower top air outlet, thereby reducing the heat transfer performance of the cooling tube bundles at tower lateral and deteriorating the overall cooling performance of the dry cooling tower.
FIG. 1 shows an existing dry cooling tower with vertical cooling delta units in an indirect air cooling power station, wherein the radiator 1 formed by cooling delta units is vertically arranged outside the bottom air inlet of the tower body 2. FIG. 2 shows a schematic arrangement diagram of an overall cross-section view of the existing cooling delta unit radiators around tower. As can be seen from FIG. 2, the radiator can be divided into 5 cooling sectors along the half tower circumference, and the whole tower has 10 sectors in total. The cooling sectors are marked clockwise in sequence along the half tower circumference: the first sector 3, covering the range of sector angle θ from 0° to 36°; the second sector 4, covering the range of sector angle θ from 36° to 72°; the third sector 5, covering the range of sector angle θ from 72° to 108°; the fourth sector 6, covering the range of sector angle θ from 108° to 144°; and the fifth sector 7, covering the range of sector angle θ from 144° to 180°. FIG. 3 shows a structural schematic diagram of the cross section of one existing cooling delta unit formed by two cooling columns. The cooling delta unit includes the first cooling column 8 and the second cooling column 9, which have the same structure and intersect with each other at their inner side end vertexes with an included angle from 40° to 60°. The outer non-intersecting sides of the two cooling columns are open to form the main air inlet 10 of the cooling delta unit, and a louver is arranged at the air inlet for controlling the air so as to prevent the cooling column tube bundle from freezing and cracking in winter.
In the absence of ambient natural crosswind, nearly all the ambient air 11 can fluently flow into the cooling delta unit along tower radial direction, and flow through the first cooling column 8 and the second cooling column 9 at the same time, so as to complete heat transfer. The air flow field structure in the cooling delta unit is symmetrical about the centerline of the cooling delta unit, and then the cooling performances of the first cooling column 8 and the second cooling column 9 are the same. However, as far as the multiple row finned tube bundles in the same cooling tube bundle of a cooling column, the finned tubes close to the louver air inlet side firstly exchange heat with the incoming flow air, so that the air temperature corresponding to the finned tubes on the downstream is raised, resulting in that the heat dissipation of the finned tubes away from the louver air inlet side is insufficient.
During the actual operation of dry cooling tower, the ambient natural crosswind always exists and causes adverse effect on the cooling performance of dry cooling tower. In order to ensure the cooling performance of dry cooling tower, the design ambient crosswind speed is usually 4 m/s or 6 m/s for the dry cooling tower. FIG. 4 shows the aerodynamic field around the cross section of one cooling delta unit in the third sector at tower lateral under the impact of 4 m/s ambient crosswind. With the influence of the 4 m/s ambient crosswind as an example, as can be seen from FIG. 4, the 4 m/s ambient crosswind causes a larger circumferential speed of the air at tower lateral. Then, for the cooling delta unit at tower lateral, the air inflow direction at the delta air inlet, namely, the louver location, deviates from the symmetry plane of the cooling unit for a certain angle of θd. Meanwhile, a large eddy is caused on the air inlet side of the first cooling column 8 of the cooling delta unit, which will certainly reduce the ventilation quantity of the first cooling column 8, weaken the cooling performance of the first cooling column 8, and eventually result in the fact that the water temperature flowing out of the first cooling column 8 is obviously increased.
Therefore, under the ambient crosswind condition, how to reduce the adverse effects of low-speed eddy areas in the cooling delta unit sat tower lateral, increase the ventilation quantity of the cooling unit, reduce or even eliminate the low-speed eddy area in the cooling unit, intensify the cooling performance of cooling tube bundles in the cooling columns and then improve the overall cooling performance of the cooling unit and the dry cooling tower have become urgent problems to be solved.